Poly (C.sub.2 -C.sub.4 alkylene terephthalate) such as polyethylene terephthalate (PET) or polybutylene terephthalate (PBT) are well known resins for a number of uses including molding applications. Such resins are frequently blended with various additives to improve properties such as impact strength, resistant to warping, resistance to oxidation, flame resistance, thermal stability etc. U.S. Pat. Nos. 3,666,716, 3,644,382 and 3,281,505 describe certain antioxidants which have been suggested for use in polyester molding compositions. U.S. Pat. No. 4,010,219 describes certain epoxy compounds which have been suggested for use in imparting improved tensile properties to polybutylene terephthalate molding compounds. The use of Poly (C.sub.2 -C.sub.4 alkylene terephthalate co-alkylene oxide) in polyester molding compositions is also known and is described for instance in U.S. Pat. No. 3,766,146. U.S. Pat. No. 4,096,202 and U.S. Pat. No. 4,034,013 describe certain impact modifiers which have been suggested for use with polyalkylene terephthalates.